Breathing apparatus with control means for the inhaled gas mixture



B. CHABANIER 3,358,681 BREATHING APPARATUS WITH CONTROL MEANS 5 Sheets-Sheet l Dec. 19, 1967 FOR THE INHALED GAS MIxTuRE Filed Oct. 22, 1965 Alim |||V Dec. 19, 1967 B. CHABANIER 3,358,681

BREATHING APPARATUS WITH CONTROL ME'ANS FOR THE INHALED GAS MIXTURE Filed Oct. 22, 1965 A 5 Sheets-Sheet 2 Dec. 19, 1967 B. CHABANIER BREATHING APPARATUS WITH CONTROL MEANS FOR THE INHALEDGAS MIXTURE Filed OCT.. 22, 1955 5 Sheets-Sheet 3 Dec. 19, 1967 v B. CHABANIER 3,358,681

I BREATHING APPARATUS WITH CONTROL MEANS FOR THE INHALED GAS MIXTURE Filed Oct. 22, 1965A 5 Sheets-Sheet 4 Dec. 19, 1967 B, CHABANlER 3,358,681

BREATHING APPARATUS WITH CONTROL MEANS FOR THE INHALED GAS MIXTURE Filed Oct. 22, 1965 5 Sheets-Sheet 5 United States Patent O 3,358,681 BREATHING APPARATUS WITH CONTROL This application is a continuation-in-part of my copending application Ser. No. 285,039, filed June 3, 1963.

This invention relates to a breathing or similar apparatus, in which the wearer inhales fresh breathing mixture and part of the mixture he has exhaled.

The terms breathing or similar apparatus are understood to mean an apparatus feeding .a breathable gas mixture into the breathing organs of the wearer; this denition includes appliances for gas anaesthesia and breathing devices for use under water or in a toxic or radioactive atmosphere.

Such appliances may, for instance, give an exclusive feed of fresh gas mixture, but this arrangement is wasteful.

Other known appliances involve the recirculating of a definite amount of gas mixture, which is inhaled every time from a variable-volume space and exhaled into the same space. The wearers breathing organs, exclusively connected to this variable-volume space, then make up with the said space, a volume which is entirely isolated from the medium and inside which the gas circulation occurs in a closed circuit.

However, it is essential that the composition of the gas remain substantially constant inside that isolated volume, in spite of the contrary effect of the wearers vital activity. Whereas it is easy to eliminate the carbon dioxide as the wearer exhales it, by means of appropriate chemicals, other means should be used to compensate for the progressive lowering of the consumed gas component or components.

Such compensation may be achieved through continuous injection of fresh gas mixture, the flow rate of the latter being sufficiently high to compensate for the largest consumption of the individual thus equipped, the said consumption varying greatly according to his activity.

When adjusted for maximum consumption, such a device involves in every other case a waste of fresh gas mixture, without any special advantage.

The apparatus according to the invention is featured by the fact that it comprises a main variable-volume space and a secondary variable-volume space, as well as an assembly of pistons or other similar parts, mechanically locked togethe-r, one of those pistons delimiting the main variable-volume space and the other delimiting the secondary variable-volume space, the main variable-volume space being connected to the wearers breathing organs, and to the secondary variable-volume space through a flap valve allowing the gas to pass only from the secondary variable-volume space to the main variable-volume space; an-d the secondary variable-volume space being connected to a source of fresh breathing mixture through a regulator, which opens the connection when the pressure inside the secondary variable-volume space is definitely lower than the pressure of the ambient medium.

As parts similar to pistons, We can mention bellows, the volume of which also varies in approximately linear fashion with the distance between their undeformable end plates. The bellows may be arranged side by side or concentrically.

As will be seen hereafter, the apparatus according to the invention make it possible to introduce, every time the wearer inhales, a volume of fresh breathing mixture 0 (not shown) of fresh breathing mixture under directly proportional to the volume inhaled at the same moment. The consumption of fresh mixture therefore varies in direct ratio to the breathing activity; it is automatically reduced when the work effected by the wearer decreases.

Some embodiments of the apparatus according to the invention make it possible to vary, in terms of the ambient pressure, the ratio between the injected volume of fresh mixture and the inhaled volume of gas mixture from previous exhalations. This makes it possible to reduce the consumption of fresh mixture when the ambient pressure rises, since the weight of the mixture then increases while its volume remains the same.

Other features and advantages are mentioned in the following specification, which refers to the appended diagrammatic drawings, in which:

FIG. 1 shows a section of an embodiment.

FIG. 2 shows a section of another embodiment.

FIG. 3 shows a section of a variation of a portion of either of the two previous embodiments.

FIG. 4 shows a section of another variation of a portion of the apparatus shown in FIG. 1.

FIG. 5 shows an embodiment wherein bellows are used for the variable volume chambers.

The apparatus shown on FIG. 1 includes a rigid housing 1, made of two assembled portions; this housing `contains two cylindrical borings with different sectional areas. In one of those borings is a piston 2 with a circular seal 3, whereas in the other boring is a piston y4 with a circular seal 5. Pistons 2 and 4 having a common axis, are linked by hollow rod 6, pierced by axial duct 7. Space 8 between both pistons inside housing 1 is connected with the outside medium through port 9.

Inside the same housing 1, pistons 2 and 4 delimit two variable-volume spaces, respectively; main space 10 and secondary space 11.

Space 10 is connected to oro-nasal mask ducts 13 and 14. Duct 13 is connected to space 10 through port 15, which lies beyond filter 15'; the latter contains a chemical which absorbs carbon dioxide. Against port 15 lies a flap valve made of a flexible tongue 16. Valve 16 is mounted so as to allow free circulation of fluid from mask 12 to space 10 and to prevent circulation from space 10 to mask 12.

On the other hand, duct 14 is connected to space 10 through port 17. Against port 17 lies another flap valve made of a exible tongue 18. Valve 18 is mounted so as to allow free circulation of fluid from space 10 to mask 12 and to prevent circulation from mask 12 to space 10.

Finally, space 10 can be connected to the outside medium through a check valve made of a disk 19. This is normally applied by spring 20, resting against cap 21 pierced by port 22, against the opening of duct 23, connected to space 10. Valve 19 connects duct 23 to the outside medium through port 22 only when the pressure inside space 10 is such that it overcomes the closing force exerted by spring 20 upon valve 19.

On the other hand, variable space 11 is connected through duct 24 to space 25 inside casing 26. The latter is made of a rigid wall, save for fexible membrane 27, fastened to the said casing along its peripheral edge.

Inside the wall of the same casing 26, port 28 connects space 25 with outside duct 29 through intermediate space 30. Inside the latter is spring 31, which applies valve plate 32 against the opening of port 28; the valve extends into space 25 through a rigid rod 33, the free end of which contacts rigid disk 34, fastened to the central portion of flexible membrane 27.

Duct 29 connects intermediate space 30 with a source an appropriate pressure and valve plate 32 is normally applied 12 through against the opening of port 28, so that the fresh mixture cannot escape into space 25.

The breathing outfit thus diagrammatically described is connected with the breathing organs of an individual through mask 12, so that the said breathing organs and the apparatus enclose a global volume separate from the outside medium.

When the assembly made of pistons 2 and 4 and of linking rod 6 is at the end of its travel in the direction of arrow 1, While at the same moment the wearer has just finished exhaling, an inhalation of the latter causes the aspiration into his breathing organs of a certain amount of the breathing mixture from space 16. The latter has a variable volume, as piston 2 moves in the direction of arrow B. Since all the walls of space are stationary, save the mobile wall formed by piston 2, the travel of the latter along the direction of arrow B is exactly proportional to the decrease of the volume of space 1G.

Since piston 4 is lixed to piston 2, its motion in the direction of arrow B is the same. The volume of space 11 is thereby increased, the increase being directly proportional to the travel of piston li, since the latter is the only mobile wall of space 11.

Therefore, a given decrease of the volume of space 10 is accompanied by a given increase of the volume of space 11. li, for instance, the sectional areas of pistons 2 and 4 are in the ratio lO/l, a decrease of x cm of the volume of space 10 is accompanied by an' increase of x/ l0 cm.3 of the volume of space 19.

Space 11 is connected both to duct 24 and to axial duct 7, which goes through linking rod 6. The fact piston 4 moves in the direction of arrow B induces a depression or lower pressure inside space 11.

The depression cannot sucl: a volume of gas into space 1i) through duct 7, because of the presence on the opening of duct 7 into space 1li of a tlap valve made of exible tongue 35, fastened to piston 2, which tongue connects duct 7 with space 10 only into the direction from duct 7 to space 10.

Therefore, the depression induced 11, can only be transmitted to closed space duct 24.

Since one wall of closed space 25 is made of flexible membrane 277 the latter is then subjected on one side to the pressure of the outside medium, while its other side is submitted to the depression inside space 25.

The said Flexible membrane is therefore shifted in the direction of arrow B, and rigid plate 34, intergral with the central portion of the membrane, pushes in the same direction the free end of rod 33, which is fastened to valve plate 32. The latter is thus moved away from the edge of port 28, which allows the fresh breathing mixture under pressure inside space 30, from outside duct 29, to penetrate into space 25 and space 11. As soon as this arrival of fresh gas mixture has restored inside spaces 25 and 11 a pressure equal to the outside pressure, flexible membrane 27 is drawn back in the direction of arrow A to its resting position by rod 33, under the action of spring 31. Valve 32 then closes the opening of port 28 and stops the arrival ot fresh breathing mixture into spaces 25 and 11.

Thanks to this characteristic arrangement of the elements of an apparatus according to the invention, at the end ot an inhalation or" the wearer into mask 12 a given volume of the breathing mixture inside space 10 of the apparatus has been introduced into the breathing organs of the wearer, while at the same time a given amount of fresh breathing mixture has been admitted into space 10 from the outside source to which the apparatus is connected.

When the wearer then exhales, the exhaled volume can only go through duct 13 and valve 16, after `having passed through iilter 1S', where the carbon dioxide is adsorbed. The volume exhaled then reaches space 1G: piston 2 and the related train are pushed in the direction oi arrow A.

as described in space 25, through l of the inhaling apparatus, the result being Piston 4 therefore compresses the fresh breathing mixture previously introduced into spaces 11 and 25, so that the said mixture is driven back through axial duct 7 in linking rod 6 and enters into space 1%, opening the flap valve made of exible tongue 35.

Every time the wearer inhales, therefore, the `global closed volume made up by the volume of the wearers breathing organs and the volume of variable space 1li takes in an additional volume of fresh breathing mixture, the latter volume being directly proportional, in a given ratio, to the volume of breathing mixture inhaled by the wearer.

The maximum volume of space 10 is such that it corresponds to the volume ot breathing mixture which the wearer can inhale at a time; the addition of a certain amount of fresh breathing mixture into the above-defined glo-bal volume has for result that, after the wearer has breathed several times and when he exhales, space 10 expands to its maximum capacity before the exhalation is over.

On the other hand, if, for some reason, the pressure inside space 10 and the connected spaces becomes lower than the pressure of the outside medium so that the pressure differential exerted on the surface of liexible membrane 27 causes the latter to move in the direction of arrow B, it will be seen that the consequence is the admission into space 2S, then into spaces l1 and 19, of a volume of fresh breathing mixture from the outside source connected to duct 29 This admission restores the pressure inside those spaces to a value equal to that of the outside pressure.

Conversely, if, for some reason, the pressure inside space 10 and the connected spaces, or inside space 11 or space 25, becomes higher than the pressure of the outside medium, the valve made of disk 19 is pushed away from the opening of duct 23. This causes the escape of a certain amount of breathing mixture, until a lower pressure is restored inside the apparatus and the breathing organs ot the wearer.

To avoid the escape through valve 19 of fresh mixture mixed with exhaled mixture, the said valve may be placed on a tapping on duct 13 between mask 12 and purifying cartridge 1S. The mixture driven back by piston 4 may also be sent more directly to the entrance of mask 12: for instance, duct 7 may be eliminated and a duct may be provided between space 11 and tube 14, with a valve operating like valve 35.

FlG. 2 shows a sectional diagram ot an embodment, according to a first variation, of a breathing apparatus incorporating various features of the invention.

Various elements of this variation are in fact the same as for the previous embodiment, and the sume reference numbers are used for both.

The difference between those two embodiments lies in the relative arrangement of some of the elements, which involves a modified mode of operation: whereas, according to the embodiment shown on FIG. l, piston 4 is related by one of its sides with space 11 of the apparatus, and by its other side with space 3 connected to the out side, on FIG. 2, the same piston t is related by one side with the outside medium and by the other with space 11,. with the difference that the latter is then on the saine side ot piston 4 as the linking rod between 2 and 4, and is separated from space 8 (which is always connected to the outside medium) by circular seal 36, lodged in a groove of a port in a wall of housing 1, thc said linking rod 5 going through the said port,

To this arrangement corresponds a modified operation however' the same as in the preceding variation.

When the assembly made of pistons 2 and l and of linking rod 6 is at the end of its travel in the direction ot arrow A, while at the same moment the wearer has just finished exhaling, an inhalation of the latter causes the aspiration into his breathing organs of a certain volume.

of breathing mixture from space 10. Piston 2 then moves in the direction of arrow B, which modifies the volume of space lil. Since all the walls of space are stationary, save the mobile wall formed by piston 2, the travel of the latter in the direction of arrow B is exactly proportional to the decrease of the volume of space 10.

Since piston 4 is fixed to piston 2, its travel in the direction of arrow B is the same. The volume of space 11 is thereby decreased, the decrease being exactly proportional to the travel of piston 4, since the latter is the only mobile wall of space 11.

Therefore, a given decrease of the volume of space 10 is accompanied by a given decrease of the volume of space 11. If, for instance, the sectional areas of pistons 2 and 4 -are in the ratio 10/1, a decrease of x cm.3 of the volume of space 10 is accompanied by a decrease of x/ l0 cm3 of the volume of space 11.

As will be seen hereafter, the said space 11 and the adjoining space 25 are exclusively filled with fresh breathing mixture `from the outside source of fresh breathing mixture under the appropriate pressure, so that the decrease of volume of space 11 causes the expulsion of a corresponding volume of fresh breathing mixture through the only possible route, i.e. into space 10, through ports 37 and axial duct 7 inside linking rod 6. Indeed, the flap valve made of flexible tongue 35, at the outside of axial duct 7 into space 10, allows the circulation of gas only in the direction from the axial duct into space 10.

Thanks to this characteristic arrangement of the various elements of -an apparatus according to the invention, at the end of an inhalation of the wearer into mask 12, a certain volume of breathing mixture from space 1t) of the apparatus has been introduced into the breathing organs of the wearer, while a certain volume of fresh breathing mixture from the outside source, to which the apparatus is connected by tube 29, has been admitted into space 10.

When the wearer next exhales, the volume exhaled can only go through duct 13 and through iiap valve 16, after having been through filter 15', where the carbon dioxide is adsorbed.

This exhaled volume then reaches space 10: piston 2 and the related train move in the direction of arrow A.

The corresponding motion of piston 4 causes an increase of the volume of space 11, i.e. induces a depression in the said space 11 and in the connected space 25.

Owing to the presence of ap valve 35, this depression can cause no aspiration of the gas mixture contained in space 1i) through axial duct 7. The only effect to this depression is that one of the sides of flexible membrane 27 is subjected to va diminished pressure, while the other side of the same membrane is connected with the outside pressure.

The said flexible membrane is then moved in the direction of arrow B, and rigid plate 34, affixed to the central portion of membrane 27, pushes in the same direction the free end of rod 33, fastened to valve plate 32. The latter is thus moved away from the edge of port 28, which allows the penetration into space 25 and space 11 of the fresh breathing mixture introduced into space 30 from outside duct 29. As soon as this introduction of fresh gas mixture has restored inside spaces 11 and 25 a pressure equal to the outside pressure, flexible membrane 27 is drawn back in the direction of arrow A to its resting position by rod 33 under the action of spring 31, while valve 32 simultaneously closes the opening of port 28 and therefore stops the arrival of fresh breathing mixture into spaces 2S and 11.

Thanks to this characteristic arrangement of the various elements of an apparatus according to the invention, when the wearer has just finished exhaling into mask 12, a new volume of fresh breathing mixture has filled space 11, replacing the mixture driven into space 10 during the immediately preceding inhalation.

It will therefore be seen that, as in the case of the previous variation, every time the wearer inhales, the global closed volume formed by the volume of the wearers breathing organs and by the variable volume of space 10 takes in an additional volume o-f fresh breathing mixture, the said additional volume being directly proportional, With a definite ratio, to the volume of breathing mixture inhaled by the said wearer.

Here also, the maximum volume of space 1) is such that it corresponds to the volume of breathing mixture that a wearer of the apparatus can inhale; but the addition of a certain amount of fresh Ibreathing mixture to the above-defined global volume involves, after the wearer has breathed several times and when he inhales, an expansion of space 10 to its maximum capacity before the said wearer has finished exhaling.

On the other hand, also as in the preceding variation, if for any reason the pressure inside space 10 and the connected spaces becomes lower than the pressure of the outside medium, the pressure differential exerted on flexible membrane 27 causes the latter to move in the directions of arrow B; it will be seen that the consequence is the admission into space 25 and into spaces 11 and 10 of a volume of fresh breathing mixture from the outside source connected to duct 29, which restores inside those spaces a pressure equal to the pressure of the surrounding med-ium.

Conversely, if for any reason the pressure inside space 10 and the related spaces, inside space 11 or space 2S, becomes higher than the pressure of the outside medium, the valve formed by disk 19 moves away from the opening of duct 23: it will be seen that the consequence is the escape of a certain amount of the breathing mixture enclosed inside the apparatus and inside the breathing organs of the wearer, until a lower pressure is restored inside those spaces.

Generally speaking, and as specified above, the breathing devices of the invention are featured by the fact that every time the wearer inhales, a definite amount of fresh breathing mixture is injected into the global closed volume formed by a variable space of the inhaling apparatus and by the volume of the breathing organs of the said wearer.

According to another feature, the amount of said fresh `breathing mixture thus injected is directly proportional, with a definite ratio, to the amount of breathing mixture inhaled or exhaled by the wearer.

According to another feature, the volume of the abovedefined variable space varies only between clearly defined limits.

According to another feature, when the volume of the above-defined variable space is minimum and the wearer inhales from the inhaling apparatus, the latter, under the action of the induced depression, automatically connects the said variable space and the breathing organs of the wearer with an appropriate outside feed of fresh breathing mixture.

According to another feature, when the volume of the above-defined variable space is maximum and the wearer exhales into the inhaling apparatus, the latter, under the action of the over-pressure which then occurs, automatically allows a sufiicient amount of the breathing mixture it contains to escape into the outside medium for the over-pressure to disappear.

The various features make novel industrial products of the breathing device considered in this patent.

Indeed, whereas known devices for breathing apparatus with semi-closed circuits also give periodic renewal of the atmosphere enclosed in a similar global closed volume, this is achieved -by means of the expulsion into the outside medium, every time the wearer exhales, of a certain amount of gas mixture contained in the said closed volume of such devices. The latter volume also includes the wearers breathing organs and the variable space inside the device, and the maximum volume of the said variable space is also at least equal to the Volume of breathing mixture which can be inhaled by the wearer from that variable space, when he inhaies very deeply. Therefore, in the case of a normal inhalation by a wearer with an average lung capacity, the said variable space is far from being completely depressed to its minimum volume at that moment. Now the known inhaling devices are such that the injection of fresh breathing mixture into their above-defined global closed volume is initiated only when the said variable space reaches its minimum volume, i.e. when the wearer inhales.

Under the usual conditions of use of such devices, whereas, every time the wearer exhales, a proportional fraction of the 4breathing mixture contained in the abovementioned global closed volume is expelled, on the other hand, fresh breathing mixture is only injected into the same global closed volume by jerks, at irregular intervals and much less frequently than the wearer inhales.

Whereas such breathing devices are used with breathing mixtures with a comparatively low ox gen content, such as air, and whereas the above-mentioned partial expulsion is purposely limited at each exhalation, so as to get the maximum yield lfrom such devices, serious risks can result for the wearer. Indeed, between the comparatively infrequent injections of fresh breathing mixture into the global closed volume of such a breathing device, there intervene comparatively long periods during which the wearer inhales exclusively the same confined atmosphere.

If, at the beginning of one of those intermediate periods, the said conned atmosphere contains a low-oxygen breathing mixture, the consumption of oxygen by the wearer can cause a temporary lowering of the oxygen content below the vital `minimum content. The one Way of eliminating7 such a risk with known inhaling devices of this type is to exaggerate purposely the rate of elimination of the breathing mixture from the global closed volume, which increases the frequency of the injections of fresh breathing mixture into the said global closed volume. However, this essential security is obtained to the prejudice of the saving of fresh breathing mixture, which greatly reduces the advantage of this type of semiclosed breathing device.

On the other hand, the breathing or inhaling apparatus which form the subject of this invention are effectively novel industrial products, since the above-mentioned risks, which can occur with known breathing devices, are entirely precluded. This feature is the consequence of their characteristic mode of operation, which ensures, every time the wearer inhales, an automatic injection of fresh breathing mixture into the global closed volume which they contain.

Thanks to the security thus afforded to the wearer, the rate of renewal provided can allow a better economy of fresh breathing mixture, without any risk for the wearer.

On the other hand, such breathing outfits, thanks to their above-defined special characteristics, have the advantage of allowing through plain and rational means and owing to their above-defined special features, a variation of the ratio of fresh breathing mixture injected, into the global closed volume of the apparatus every time the wearer inhales.

This possibility, which is of interest notably when the breathing apparatus is used in a surrounding medium with an absolute pressure different from the normal atmospheric pressure, is yet another feature of the breathing apparatus of the invention.

More explicitly, let us admit that a semi-closed breathing apparatus partly refreshes the global closed volume it contains every time the wearer breathes, by introducing a volume of fresh breathing mixture corresponding for instance to one tenth of the volume inhaled or exhaled by the wearer. Let ns also admit that this lfm rate of renewal is normally sufficient, ailowing for the wearers oxygen consumption, for the composition of the breathing mix- S ture enclosed in the global closed volume of the apparatus to remain unchanged.

lf this is the case when the pressure of the ambient medium is equal to atmospheric pressure, this ceases to be the case when the pressure of the said medium varies. Indeed, if the pressure of the said outside ambient medium is doubled, for instance, the volumetric rate of renewal built into the breathing apparatus is not altered, but the effectiveamount of fresh breathing mixture, measured at atmospheric pressure, injected into the global closed volume of the breathing apparatus is then doubled. In the same fashion, when the pressure of the outside medium is trebeld, the effective amount of fresh breathing mixture injected is trebled, and so on.

Since the rate of oxygen consumption of the wearer or the apparatus is not altered by such an increase of pressure of the outside medium, the consumption of fresh breathing mixture is therefore doublde or trebled, for instance, without any advantage ensuing.

lf the source of fresh breathing mixture is made of cylinders containing gas under pressure and provided with the breathing apparatus, the time of use of this equipment is proportionately reduced, without any other reason.

On the other hand, the characteristic arrangement described above, according to which the variation of the amount of fresh breathing mixture introduced into a breathing apparatus of the invention is a function of the variation of pressure of the ambient medium, is a novel means of saving fresh breathing mixture under the same conditions.

Thanks to this characteristic arrangement, the breathing outfits considered in this patent automatically vary the proportion of fresh breathing mixture injected into a breathing apparatus of the invention according to the ambient pressure, through recirculating more or less of the breathing mixture contained in the global closed volume of such a breathing or inhaling apparatus.

To this end, an additional amount of fresh breathing mixture from the global closed volume of a breathing apparatus of the invention can be recirculated only when an injection of fresh breathing mixture occurs into the said global volume, the passage(s) through which this recirculation exclusively occurs being normally obturated, and the opening of the same being controlled by an appropriate mechanism actuated directly or indirectly, exclusively by and during the said injection of fresh breathing mixture.

With this characteristic arrangement, not only does the injection of fresh breathing mixture into an inhaling apparatus of the invention make possible the said recirculation of the breathing mixture contained in the said global closed volume of the said apparatus, but it also effects such recirculation when needed.

To achieve this characteristic arrangement, a recirculation of the breathing mixture contained in the global closed volume of an inhaling apparatus of the invention is caused by means of the dynamic energy resulting from the injecting pressure of the fresh breathing mixture into the said apparatus; an appropriate arrangement of the port(s) through which the injection occurs automatically ensures the injection, according to the pressure of the ambient medium.

FIG. 3 shows a diagram of an embodiment of such a recirculating mechanism.

Since this mechanism involves only the elements of a breathing apparatus of the invention which are more particularly brought into play for the injection of fresh breathing mixture into the apparatus from an outside source (not shown), FIG. 3 shows only the portion of a breathing apparatus of the invention containing those elements.

As previously described, space 25 of this portion of a breathing apparatus is connected to metering space 11 of the same apparatus.

A depression inside space 2S comparatively to the outside medium causes flexible membrane 27 to move towards the bottom of casing 26; consequently, Valve 32, integral with rod 33, is pushed away from the edge of port 28, against which it is normally applied by spring 31. The fresh breathing mixture coming from an outside source (not shown) through duct 29 can then go through port 28.

In the case of FIG. 3, the fresh breathing mixture cannot directly enter space 25, owing to the presence of flexible obturator 37 around rod 33, and is deected towards closed space 38.

The latter is bounded by wall 26 of the casing and by flexible membrane 39, the periphery of which is pressed between this wall and element 40.

Inside element 4t), on the opposite side of flexible membrane 39, is space 41, which is Aconnected to variablevolume space lil of the inhaling apparatus through duct 42 The free central portion of membrane 39 is integral with circular plate 43, which is integral with rod 44. The latter projects into element 39 and goes through port 45, which connects space 41 to cylindrical space 46. The latter ends in a nozzle 47, connected to space 25.

Cylindrical rod 44 carries flange 48, normally applied against the edge of port 45 under the action of spring 49, which is lodged inside space 41 between the end plate of the said space and circular plate 43.

Consequently, cylindrical rod 44 is pushed by sprin-g 49 in the direction of arrow C, and flange 48 prevents any communication between space 41 and space 46, i.e. between duct 42 and space 25.

When, as indicated above, the depression inside space 25 initiates an admission into closed space 38 of fresh breathing mixture Iunder pressure, various actions occur.

The said fresh breathing mixture under pressure tends to go through axial duct 50 of cylindrical rod 44, escaping both through side port 5l and through end port 52.

The sectional areas of both ports having been suitably designed, the resultant metering of the flow of fresh breathin-g mixture under pressure raises the pressure of the said mixture inside axial duct 50 of rod 44 and inside space 38.

The overpressure then exerted upon the side of flexible membrane 39 related to space 38 is such that the force exerted on the said flexible membrane in the direction of arrow D is higher than the force exerted in the opposite direction by spring 49, so that the said flexible membrane and the integral cylindrical rod 44 are pushed in the direction of arrow D. Flange 48 of the said cylindrical rod is then moved away from the edge of port 45, and free communication is established between space 41 and space 46.

On the other hand, the stream of fresh breathing mixture issuing from end port 52 is so directed that it moves along the axis of nozzle 47 before it reaches space 25. An aspiration is thus induced inside space 46 of element 40, which causes the movement into space 25 of a stream of breathing mixture from variable-volume space of the inhaling apparatus through duct 42. The flow is limited by the sectional area of port 45, and also by the presence of side port 51. Indeed, part of the stream of fresh breathing mixture under pressure going through axial duct 50 of cylindrical rod 44 also escapes through side port 51, which is so directed that the stream of gas issuing from it is not `directed towards nozzle 47.

In practice, the various parameters, sectional areas of port 45, of nozzle 47, of ports 51 and 52, among others, are so calculated that, for a given feeding pressure of fresh breathing mixture into space 38, the amount of breathing mixture introduced into space 25 through port 45 is zero when the pressure of the ambient medium is equal to the atmospheric pressure. In other words, in that case, only fresh breathing mixture from the outside source connected to duct 29 is fed into space 25, therefore into space 11 of the inhaling apparatus. Under such conditions, there is no dilution or supplementary recirculation. The ratio between the amount of fresh breathing mixture injected into space 10 every time the wearer breathes and the amount of breathing mixture inhaled or exhaled is therefore the nominal ratio which corresponds to the characteristics of the apparatus.

On the other hand, a different result is obtained when the same inhaling or breathing apparatus is placed in a medium at a pressure above atmospheric pressure.

In that case, the initiation of an admission of fresh breathing mixture (at a pressure above atmospheric pressure) also causes overpressure inside axial duct 50. The increased specific weight of the fresh breathing mixture raises the pressure drop across ports 51 and 52; but at the same time, the efficiency of the injecting action through nozzle 47 is increased, so that the suction into space 46 is then greater. The ow through side port 5] `then becomes insufficient to cover this suction, which also carries along a proportion of breathing mixture from the variable-volume space of the inhaling apparatus through duct 42 and port 45.

A dilution is then achieved, which corresponds to an additional recirculation of the breathing mixture.

There results a decrease of the effective amount of fresh breathing mixture injected into the inhaling apparatus every time the wearer breathes, this decrease being the larger as the above-described phenomena become more pronounced, i.e. as the pressure of the ambient medium increases.

Through suitable choice of the parameters (size of the varioius ports and passages), and through suitable calculation of the nozzle and of the overpressure of the fresh breathing mixture compared with the ambient pressure, the variation of the theoretical injection ratio of fresh breathing mixture into a breathing apparatus of the invention may be made directly proportional to the value of the ambient pressure.

It should be noticed that the above-described embodiment effectively corresponds to the above-defined characteristics.

Indeed, a possible alteration of the injection ratio of fresh breathing mixture, through dilution with the breathing mixture contained in the variable-volume space of a breathing apparatus of the invention, can only occur once the injection of fresh breathing mixture has been initiated. It is the very pressure of this injection of fresh breathing mixture which causes the opening of the passage through which the dilution can occur.

On the other hand, the dilution does not occur of its own accord, but only under the action of a depression caused by the injection of fresh breathing mixture, the dilution being varied by the alteration of this depression according to the effective pressure of the ambient medium in which the breathing apparatus is immersed.

Different arrangements and embodiments are sible within the scope of the invention.

The automatic variation of the dilution allows in fact a very important saving of fresh breathing mixture, the larger as the pressure of the ambient medium is higher above atmospheric pressure.

Generally speaking, the arrangements given as examples in this specification are nowise restrictive of this invention which also relates to every other arrangement or embodiment within its scope.

In particular, the above-mentioned ratio between the sizes of spaces 10 and 11 of breathing apparatus is purely indicative. The suitable value of this ratio depends on the conditions of use of such an apparatus, but also on the nature of the breathing mixture used. The latter can be either pure oxygen, or air, or a synthetic mixture, or any other suitable breathing mixture.

The connection between an inhaling apparatus of the invention and the wearers breathing organs, indicated examplewise as being ensured by means of an oro-nasal also posmask, may be achieved by any other means or method leading to the same result. Also, the flap valves may be arranged in any other fashion, as well as the variablevolume spaces. The latter may quite as well be contained in bellows which deform in one direction only, or according to any other suitable embodiment.

The location of the filter containing a carbon dioxide absorber may be altered, as also the location of the exit valve for overpressure. The latter may advantageously be so located that when the breathing mixture is expelled through the said valve, freshly exhale-d breathing mixture not havin-g gone through the chemical filter is expelled through it. This allows a saving of the chemical in the lter.

he admission of fresh breathing mixture into the variable-volume space of a breathing apparatus of the invention may also be arranged so that the wearer always inhales in priority the fresh mixture thus injected.

The source of fresh breathing mixture may be chosen at will, provided only that the feeding pressure at the inlet of the inhaling apparatus is higher than the ambient pressure. In the case when the inhaling .apparatus is used in a variable-pressure medium, a pressure controller is placed between the source of fresh breathing mixture and the apparatus; the controller automatically varies the feeding pressure of the said mixture, so that it always remains above the pressure of the outside medium by the same amount.

The escape towards the ambient medium of an excess of breathing mixture exhaled by the wearer into the main variable-volume space l@ of an inhaling apparatus of the invention may be ensured, not by a calibrated check valve 19 as above, but by a controlled valve, shown at 70. Such a valve 70 is then so arranged that when the volume of the main variable-volume space lil of a breathing apparatus reaches about its maximum capacity, the corresponding movement of the mobile wall 2 of the said main variable space actuates through a chain '72 the temporary opening of valve 70. Since the said controlled valve opens only when the main variable-volume is near its maximum, only the desired escape can occur. The said controlled valve 70 closes as soon as the main variable volume space ceases to be dilated to near its maximum capacity. FIG- URE 2 shows both valves 19 and 70 in order to illustrate also the controlled valve. One only of these valves practically would be provided on a breathing apparatus.

FIG. 4 shows another variation, which makes it possible to alter the amount of fresh breathing mixture introduced when the wearer inhales; the alteration of the addition ration of fresh breathing mixture is automatically ensured in terms of the pressure of the outside medium.

The breathing apparatus shown on FIG. 4 (diagrammatical section) is similar on the whole to the apparatus described in connection with FIG. l, and the common elements have the same reference numbers.

However, the embodiment shown on FIG. l involves only one secondary variable-volume space 11 inside enclosure 1 of the apparatus, whereas, according to the arrangement of the embodiment shown on FIG. 4, there is another secondary variable-volume space 11. Piston 2 of the inhaling apparatus shown is iixed to two pistons 4 and 4', through linking rods 6 and 6', provided with axial ducts 7 and 7.

Circular or toroidal seals 5 and 5 are located in peripheral grooves of pistons 4 and 4.

Pistons 4 and 4 are shown with equal sectional areas but their sectional areas may be different.

As said in connection with the example described on FIG. l, space 1l is connected with main variable-volume space 19 of the inhaling apparatus through axial duct 7 of linking rod 6; a tlap valve made of exible tongue 35 allows the passage of iluid only from space 11 into space It?.

The same space l1 is also connected, through duct 3ft,

l2 with inside space 25 of a controlling device, one wall of which is a flexible diaphragm 27.

Similarly, space 11 is conneted with main variablevol time space 10 ofthe same apparatus through axial duct 7 of linking rod 6", a flap valve made of flexible tongue 35' allows the passage of fluid only from space 11 into space 10.

The same space 11 is also connected through duct 24 with the same inside space 2S of the same controlling device.

On the other hand, the same space 11' is also connected with duct 53, at the end of which is fastened casing 54, the inside circular boring of which is separated from duct S3 by transverse wall 55. Inside this boring is piston 56, with seal 57. Between one side of this piston and transverse wall is internal space 58, connected with the outside medium through port 59 in the wall of casing 54, whereas between the end plate of casing 54 and the other side of piston 56 is another space 60, which is completely closed.

Piston 56 is fixed to the rod of valve 61, which rod goes through transverse wall 55.

When valve 61 is applied against the edge of the opening of duct 62, which opens into duct 53, the connection between space 11 and space 10 is interrupted.

According to a characteristic of this embodiment, the closing of duct 52 by valve G1 is so ensured that, by means of a mechanism to be described hereafter, a connection through duct 62 is ensured between spaces 10 and 11 as soon and as long as the pressure of the outside medium is equal to, or higher than, a predetermined value.

In the present example, this result is obtained by the fact that a permanent pressure is exerted on piston 56 by the gas inside space 60 of casing 54. This pressure is established by a previous injection of gaseous fluid through an opening which is normally closed by air tight plug 63.

This pressure thus exerts a known and permanent force on one side of piston 56, in the direction of arrow B. The pressure may be replaced by the action of a spring which pushes piston S6 to the right: the latter then has no need to be airtight.

As long as the pressure of the outside medium, exerted on the other side of the same piston inside space 58 of casing 54 through port 59, does not reach such a value that it exerts on piston 56 a force in the direction of arrow A greater than the above-defined force, the said piston and valve 61 are pushed as far as possible in the direction of arrow B; i.e. valve 61 is then applied against the edge of the opening of duct 62, which is closed.

Conversely, it will be seen that when the pressure of the outside medium is such that it exerts on piston 56 a sufficient force in the direction of arrow A, piston 56 and valve 61 are moved at the same time in the direction of arrow A. Duets 53 and 62, i.e. spaces 11 and 10 of the inhaling apparatus, are then connected.

The result is that if the apparatus thus built is located in an outside medium at atmospheric pressure, it will work exactly as described lfor the example shown on FIG. l. indeed, variable-volume spaces 11 and 11 can then be assimiliated to one similar space, the mobile wall of which would have a sectional area equal to the sum of the sectional areas of the mobile walls of those spaces 11 and 1i.

As specied above, the ratio between the sectional area of the mobile wall of this secondary variable spaceaccording to the arrangement shown, between the sum of the sectional areas of pistons 4 and 4-and the sectional area of the mobile wall of the main variable space, i.e. of piston 2, controls the rate of renewal, through the introduction of fresh breathing mixture every time the the wearer breathes, of the breathing mixture enclosed in the global closed volume made of main variable space lll and of the wearers breathing organs.

If this ratio is 1/10, for instance, every time the wearer 13 exhales into main variable space 10, the amount of fresh breathing mixture-from the source of such mixture connected to duct 29-simultaneously injected into the same space will be one tenth of the volume exhaled.

If the breathing apparatus shown in FIG. 4 is now supposed to be located in an outside medium at such a pressure as to cause the opening of the above-mentioned connection between space 11 and spa-ce 10 of the said apparatus, the operation of the apparatus is altered.

Indeed, when the wearer inhales from space 10, the corresponding movement of piston 2, and therefore of pisons 4 and 4', in the direction of arrow B, gives modified results.

As regards space 11, nothing is altered: the depression induced in that spa-ce and transmitted to space 25 of the controlling device through duct 24 causes the arrival into space 11 of a sucient amount of fresh breathing mixture for the pressure to be restored to the value of the outside ambient pressure.

On the other hand, the depression simultaneously taking place inside space 11 can then cause the suction of breathing mixture from main Variable space through ducts 53 and 62.

A flap valve made of flexible tongue 64 is placed between duct 24 and space 11. This valve allows the passage of fluid from duct 24 into space 11', but it is so designed as to offer such a resistance that when passage is also possible between space 11 and main variable space 10, circulation between those two spaces only is then induced by the depression inside spa-ce 11.

Incidentally, the same result might be reached through positive closing of the connection between duct 24 and space 11 when valve 61 opens the connection between ducts 53 and 62, and vice versa.

The result is that when the wearer now exhales, the movement of piston 2 in the direction of arrow A causes the introduction into space 10 of a certain amount of fresh breathing mixture from space 11, and also of a certain amount of breathing mixture from spa-ce 11'. As the latter space is now filled with breathing mixture from main variable space 10, the result, as regards space 11', is a mere recirculation inside the breathing apparatus.

If the sectional areas of pistons 4 and 4 are the same, the amount of fresh breathing mixture is then twice smaller, compared with the amount expired by the wearer.

If the opening of the connection between spaces 11' and 10, which thus modifies the operation of the 'breathing apparatus, occurs automatically when the pressure of the outside medium reaches twice the atmospheric pressure, for instance, it will be seen that the injection ratio of fresh breathing mixture, which was previously supposed to be 3%@ when the pressure of the ambient medium was equal to atmospheric pressure, is only 3%0 under those conditions. j

If it is supposed that an injection ratio of fresh breathing mixture of 3/10 into the main variable space of the inhaling apparatus ensures sufficient compensation of the oxygen consumption of the wearer in an outside medium at atmospheric pressure, the doubling of this pressure, the injection ratio remaining the same, would double the amount of fresh breathing mixture injected, the said amount being computed as the volume in the open air.

There would therefore be a waste of fresh lbreathing mixture, since the oxygen requirements of the wearer do not vary with the ambient pressure.

On the other hand, the fact that the injection ratio is altered from 1/10 to 1/20 when the ambient pressure is doubled approximately ensures the constancy of the amount of fresh breathing mixture effectively injected, computed as the volume in the open air. There is no more waste of fresh breathing mixture, without the safety of the diver being jeopardized.

It should be noticed that the example shown on FIG. 4 is merely indicative, notably as regards the number of secondary variable spaces.

This example involves on one hand a secondary variable space 11, which can be fed by suction exclusively with fresh breathing mixture from pressure controller 26, and on the other hand a secondary variable space 11', which can be fed by suction, either with fresh breathing mixture from the same controller, or with breathing mixture lfrom the main variable space of the inhaling apparatus, according as the pressure of the ambient medium is lower or higher than a given value; but this examplev nowise restricts the described embodiment.

The latter may quite as well involve on one hand a secondary variable space 11 as dened above, and ltwo or several secondary variable spaces 11 also as defined above, each one of the latter being fed by suction, either exclusively with fresh breathing mixture from controller 26, or exclusively with mixture from the main variable space of the inhaling apparatus, the change from one feed to the other occurring -for a definite value of the pressure of the ambient medium for each secondary space.

We may thus visualize, for instance, an inhaling apparatus containing on one hand a secondary Variable space 11, always fed with fresh breathing mixture, and on the other hand two secondary variable spaces 11', all three spaces having mobile walls with a global sectional area equal to the sectional area of the mobile wall of secondary space 11 of FIGS. l and 2.

Suitable mechanisms, e.g. similar to the one indicatively shown in FIG. 4, then respectively control the feed of those secondary variable spaces 11 either with fresh breathing mixture of with breathing mixture recirculated from the main variable space of the same inhaling apparatus, the said mechanisms being so adjusted that they are actuated by different pressures of the ambient medium. According to the above-mentioned indicative example, if for instance the predetermined injection ratio of fresh breathing mixture is 1/10 when the ambient medium is at atmospheric pressure, the said ratio may become 1/20 for instance when the pressure is doubled and 1/30 when the pressure is trebled.

Obviously, other injection ratios of fresh breathing mixture land other variations of the said ratios with the pressure of the ambient medium may be chosen; on the other hand, the number of secondary variable spaces is nowise restricted.

Furthermore, a mechanism sensitive to the value of the pressure of the outside medium may be arranged otherwise than shown indicatively on FIG. 4; notably, airtight pressurized space 60 can be replaced by any suitable means, such as a capsule, an elastic bellows or a suitable spring. As indicated above, this mechanism can not only control the opening or closing of the connection between secondary variable space 11 and main varia-ble space 10 of the same breathing apparatus, as shown on FIG. 4, but it also can control the simultaneous closing or opening of the connection between the said space 11- and inside space 25 of the pressure controller. In the latter case, calibrated flap valve 64 becomes useless.

The variable-volume spaces here diagrammatically shown as cylinders, with a piston as the mobile wall, may also be carried out in any other fashion, notably as bellows deforming in one direction only, through the movement of one of their Walls.

FIG. 4 shows the arrangement applied to the embodiment shown on FIG. l. The same arrangement may be applied to the embodiment of FIG. 2: the application is sufficiently obvious to make a description superfluous.

The arrangement shown on FIG. 4 may be used with breathing or inhaling apparatus with a different mode of operation. This arrangement can indeed bring appreciable advantages to inhaling apparatus which achieve, by other methods than the ones considered here, the partial renewal of the atmosphere inside their closed volume. When the characteristic arrangement of FIG. 4 can be applied with advantage to such apparatus, this arrangement makes it possible to eliminate the waste due to l5 the constant rate of renewal when the pressure of the ambient medium is higher than the value for which the said rate has been computed` Generally speaking, the arrangement considered relates to all the modes of operation of breathing apparatus using a rate-controlling space for the partial renewal of the atmosphere inside their global closed volume; the division of the said rate-controlling space into multiple rate-controlling spaces, and the cutting out of one or several of those spaces according to the pressure of the outside medium, are characteristics relating to FIG. 4.

lt should be noticed that the arrangement considered makes it possible, not only to maintain a constant composition of the breathing mixture enclosed inside the global voiume of an inhaling apparatus, but also to vary the composition of the said mixture according to a predetermined variation of the pressure of the outside medium. It was supposed above, as a non-restrictive example, that the amount of fresh breathing mixture injected into the global closed volume was varied proportionately to the variation of the pressure of the outside medium. However, the amount may be varied otherwise than proportionately, and differently according to the value of the pressure of the ambient medium.

FKGURE 5 shows a breathing apparatus similar to the one represented on FIGURE 4 except that the variable spaces are surrounded by bellows w12, 1M, 1% instead of cylinders and pistons. A movable wall 153 of the bellows plays the part of pistons 2, their connecting ducts 7, 7. Tube 62 opens into the xed end wall of chamber it) instead of the lateral wall due to the flexibility of the latter but functions in the same fashion.

Another possibility for varying the rate of recirculation of the expired mixture consists in providing fresh mixture only to the wearer when he is at the surface or near the surface, which usually occurs during comparatively short periods only. This makes it possible to reduce the proportion of fresh mixture injected, since the said mixture is mixed with exhaled mixture only when its pressure is definitely above atmospheric pressure.

What i claim is:

1. An inhaling or similar apparatus comprising a main variable-volume chamber, a plurality of secondary variable-volume-chambers, means interconnecting said variable-volume chambers at one wall of each chamber, a breathing mask, conduit means connecting said breathing mask with said main variable-volume chamber and said main variable-volume chamber with said secondary variable-volume chambers, check valve means for aliowing the passage of gas from said secondary variablevolume chambers into the main variable-volume chamber; a source of fresh breathing mixture, conduit means connecting said secondary variable-volume chambers to said source of fresh breathing mixture, controller means responsive to the pressure in one of said secondary variablevolume chambers for controlling the how of fresh mix` ture to said chamber when the pressure therein is lower than the ambient pressure, and means feeding the other of said secondary variable-volume chambers with gas exhaled from said mask and with fresh breathing mixture in accordance with a predetermined ambient pressure, the ratio of said exhaled gas to said fresh breathing mixture in terms of volume increasing with an increase in ambient pressure.

2. An apparatus as in claim 1 wherein the intercon- 4, Li' and of l5 necting means and conduit means are connected to provide a change in the volume of the chambers as the interconnecting means move.

3. An apparatus as in claim 1 wherein the interconnecting means and conduit means are connected to provide an increase in the volume of one chamber and a decrease in the volume of the other chambers as the interconnecting means move in the same direction.

1i. An apparatus as in caim 1 further including carbon dioxide absorption means in the conduit means connecting the breathing mask and the main variablevolume chamber.

5. An apparatus as in claim i. further including check valve means for connecting the main variable-volume chamber and breathing mask to the ambient medium in which the mask is used when the pressure in the chamber exceeds the pressure of the medium.

e. An apparatus as in claim 1 further including means for connecting the main variable-volume chamber and breathing mask to the ambient medium in which the mask is used when the voiume of the main variablevolume chamber exceeds a predetermined value.

'7. An apparatus as in ciaim further comprising means responsive to the ambient pressure in which the mask is used for varying the ratio of the volume of fresh breathing fluid mixture to the volume of exhaled mixture.

8. An apparatus as in claim 1 in which said variablevolurne chambers are flexible-walled chambers.

9. An apparatus as in claim 1 in which said variablevolume chambers are bellows-like construction.

lil. An apparatus as in claim l further comprising stop means for stopping the feed of exhaled mixture when the introduction of fresh breathing mixture ceases.

i1. An apparatus according to claim 1 further cornprising an aperture formed in said conduit means connecting the secondary variable-voiume chamber to the source of fresh breathing mixture, a chamber surrounding said aperture, and conduit means connecting the interior of sadchamber with the main variable-volume chamber, said aperture formed in said conduit means directing the flow of said fresh breathing mixture to the opening of said surrounding chamber.

i2. An apparatus according to claim 11, further comprising stop means for stopping the feed of exhaled mixture when the introduction of fresh breathing mixture ceases.

13. An apparatus according to claim 1i, further cornprising at least one supplementary aperture in the said conduit means connecting the secondary variable-volume chamber to the source of fresh breathing mixture, said supplementaryy aperture directing mixture to the inner wall of said surrounding chamber.

References Cited UNITED STATES PATENTS 2,217,575 itl/i940 Van Hoff 12S-202 2,834,343 5/1958 Keckler et al. 12S-142.5 3,916,053 l/ i962 Medovick 12S- 146.5 3,068,864 12/1962 Tietze 12S-M4 3,149,631 9/l964 Svenson 12S-142.2 3,256,826 6/ i966 Eian t28-145.8

o RlCHARD A. GAUDET, Primary Examiner.

ROBERT E. MORGAN, Examiner. W. E. KAMM, Assistant Examiner, 

1. AN INHALING OR SIMILAR APPARATUS COMPRISING A MAIN VARIABLE-VOLUME CHAMBER, A PLURALITY OF SECONDARY VARIABLE-VOLUME-CHAMBERS, MEANS INTERCONNECTING SAID VARIABLE-VOLUME CHAMBERS AT ONE WALL OF EACH CHAMBER, A BREATHING MASK, CONDUIT MEANS CONNECTING SAID BREATHING MASK WITH SAID MAIN VARIABLE-VOLUME CHAMBER AND SAID MAIN VARIABLE-VOLUME CHAMBER WITH SAID SECONDARY VARIABLE-VOLUME CHAMBERS, CHECK VALVE MEANS FOR ALLOWING THE PASSAGE OF GAS FROM SAID SECONDARY VARIABLEVOLUME CHAMBERS INTO THE MAIN VARIABLE-VOLUME CHAMBER; A SOURCE OF FRESH BREATHING MIXTURE, CONDUIT MEANS CONNECTING SAID SECONDARY VARIABLE-VOLUME CHAMBERS TO SAID SOURCE OF FRESH BREATHING MIXTURE, CONTROLLER MEANS RESPONSIVE TO THE PRESSURE IN ONE OF SAID SECONDARY VARIABLEVOLUME CHAMBERS FOR CONTROLLING THE FLOW OF FRESH MIXTURE TO SAID CHAMBER WHEN THE PRESSURE THEREIN IS LOWER THAN THE AMBIENT PRESSURE, AND MEANS FEEDING THE OTHER OF SAID SECONDARY VARIABLE-VOLUME CHAMBERS WITH GAS EXHALED FROM SAID MASK AND WITH FRESH BREATHING MIXTURE IN ACCORDANCE WITH A PREDETERMINED AMBIENT PRESSURE, THE RATIO OF SAID EXHALED GAS TO SAID FRESH BREATHING MIXTURE IN TERMS OF VOLUME INCREASING WITH AN INCREASE IN AMBIENT PRESSURE. 